This research program is studying the physiology of the ocular and neck reflexes that control gaze, and the specific role of the cerebellar nodulus and uvula in producing these reflexes. Gaze reflexes are necessary for clear vision because they steady the head and keep the eyes pointed in a constant direction as the head moves. Vision is poor and balance unstable without gaze reflexes. The cerebellum is critical to proper operation of gaze reflexes, but only the lateral vestibulocerebellum, or flocculus, has been extensively studied. The neural inputs and outputs of nodulus and uvula imply a vestibular function in gaze reflex control, yet most studies of cerebellar roles in gaze reflexes have neglected nodulus and uvula. Research during the firest three years of this research program has made important advances in describing properties of the gaze reflexes in which nodulus and uvula participate, documenting deficits in vestibulo-ocular and optokinetic gaze reflexes after nodulus-uvula lesions, and recording neuronal activity in nodulus and uvula. We will extend our findings in three areas and add a fourth area of emphasis. 1) We will continue to explore normal gaze reflexes, expanding our studies to include vestibulo-ocular responses to stimuli that especially excite nodulus-uvula neural activity. 2) We will further characterize simple spike responses of nodulus-uvula Purkinje cells, searching for properites that distinguish these cerebellar responses from other cerebellar response. We will also record nodulus-uvula neural activity during short term vestibular reflex adaptation procedures. 3) We will extend our studies of the effects of nodulus-uvula lesions on gaze reflexes and their adaptive capacity. 4) We will add recording and lesion studies that directly compare nodulus-uvula neural responses or lesions to those of cerebellar flocculus. This will test the hypothesis that nodulus and uvula participate primarily in ongoing gaze reflexes while flocculus functions primarily in adaptive control of gaze reflexes. The results of the proposed experiments will give us further insight into the functions of the cerebellum in motor behavior and the different roles of medial nodulus-uvula cerebellum and lateral cerebellar flocculus. We hope also for further insight into basic reflex functions, adaptation to disturbed sensory inputs, and recovery from neurological disorders caused by brain damage.